Linings for steel ingot molds and foundry molds

ABSTRACT

A LINING FOR A METALLURGICAL MOLD COMPRISING A LAYER OF AN AGGLOMERATED MIXTURE OF REFRACTORY PARTICLES OF A MEDIUM PARTICLE SIZE, OF FIBERS, AND OF A SMALL AMOUNT OF AN EXOTHERMIC MIXTURE OF A SMALL PARTICLE SIZE, SAID MIXTURE BEING AGGLOMERATED BY MEANS OF A SYNTHETIC RESIN.

H. NOU VEAU 3,582,369

LININGS FOR STEEL INGOT MOLDS AND FOUNDRY MOLDS 7 June 1, 1971 FiledJuly 18, 1968 INVENT OR Han/RY NOUVEAU ATTORNEYS United States Patent OInt. Cl. lizsb 7/36 U.S. Cl. 106-38.22 1 Claim ABSTRACT OF THEDISCLOSURE A lining for a metallurgical mold comprising a layer of anagglomerated mixture of refractory particles of a medium particle size,of fibers, and of a small amount of an exothermic mixture of a smallparticle size, said mixture being agglomerated by means of a syntheticresin.

This application is a continuation-in-part of application Ser. No.522,648, filed Jan. 24, 1966, now abandoned.

BRIEF SUMMARY OF THE INVENTION The present invention relates to liningsused in steel ingot molds and foundry molds to retard the solidificationof the metal of the casting undergoing solidification.

It is more particularly concerned with exothermic linings for thispurpose, comprising mixtures which participate in an exothermic reactionat the elevated temperature of the molten metal.

It has already been proposed to provide such exothermic linings, andnumerous compositions have been suggested for this purpose. However,their cost is so high that they cannot be economically employed if alining of appreciable thickness is to be applied.

Moreover, the thermal conductivity of a given wall is a function of itstemperature and increases rapidly with temperature. It results that anexothermic lining which attains high temperature also becomes a verygood conductor of heat from the cast metal to the metal wall of themold, with serious heat loss. It has been proposed, therefore, to remedythis difiiculty by providing an insulating layer between the exothermiclayer and the metallic wall of the mold.

Such an insulating layer must satisfy a number of requirements. It musthave a heat capacity and heat conductivity as small as possible so as,on the one hand, to reduce the heat flow therethrough and, on the otherhand, to reduce the quantity of heat taken away from the metal or fromthe exothermic material. These two conditions dictate an insulatinglining which is porous and of low density. At the same time, however,the insulating lining must have sufficient mechanical strength; and thislast is especially desirable during fabrication and installation of thelining.

The present invention is the result of studies conducted with a viewtoward improving the nature of those layers which serve as insulatinglayers in mold linings. The present invention has for its objects theprovision of a porous insulating lining of fine porosity providing a lowcoefiicient of heat transfer, which thus attains a high temperature dropacross the insulating lining and avoids large heat transfer from themetal or fromv the exothermic layer but which nevertheless has adesirable compactness which results in satisfactory mechanical strength,in contrast to the usual high porosity of thermal insulators.

"ice

BRIEF DESCRIPTION OF THE DRAWING The drawing shows a somewhat enlargedfragmentary cross-sectional view of a lining of the present invention inplace on a mold wall.

DETAHLED DESCRIPTION The invention comprises the provision of a moldlining including a layer constituted by an agglomerated mixture of 60 toparts in weight of refractory particles having an A.F.S. index lowerthan and, interspersed in the interstices between said refractoryparticles, 7 to 15 parts in weight of particles having 70 mesh fineness,of a combustible organic material of natural vegetable origin, such asflaked husks, crushed husks, flakes from grain hulls, crushed residuesof oil seeds, broken residues of oil seeds, pulps, fine sawdust and woodflour, 2.5 to 6 parts in weight of particles of readily oxidizablematerial selected from the class consisting of silicon-calcium alloysand siliconaluminium alloys and 2 to 7 parts by weight of particles ofan oxidizer selected from the class consisting of manganese dioxide andiron oxide, said particles of oxidizable material and oxidizer having anA.F.S. index higher than 100. In speaking of 70-mesh fineness and thelike, it is meant that substantially all the material will pass througha 70-mesh screen.

The layer of lining according to the present invention comprises arefractory network structure, and in the interstices of this structureare combustible materials and an exothermic mixture. It results thatthis layer has a compactness that gives the necessary mechanicalstrength but that, during the teeming of the metal, the exothermicmixture will ignite and will supply this layer with the heat necessaryto maintain its temperature and simultaneously ignite the combustibleconstituents which burn with the entrapped air and give off hotinsulating gases that occupy the finely porous network that thecombustion of the said constituents creates in the mass of the layer.

The lining of the present invention thus is characterized by relativelylarge refractory particles, with their interstices filled withrelatively small particles of combustibles and readily oxidizablematerials and oxidizers therefor.

The lining according to the invention plays in consequence and insuccession the triple role of a mechanically resistant layer duringinstallation and teeming, of a semiexothermic layer thereafter, andfinally of an insulating layer until the final solidification of themelt. It is also to be noted that the total reaction time should besubstantially less than the solidification time for the ingot.

The layer according to the present invention may be utilized eitheralone or in combination with a more highly exothermic layer or with alayer more exclusively refractory in nature. Such a more highlyexothermic layer comprises from 3 to 35 parts in weight of a readilyoxidizable material and from 8 to 22 parts in weight of an oxidizertherefor having an A.F.S. index higher than 100, 8 to 12 parts in weightof particles having a 70 mesh fineness of a combustible organic material20 to 78 parts in weight of refractory particles having an A.F.S. indexlower than 100 and up to 11 parts of asbestos fibers.

As the refractory substances that may be used in the construction ofsuch layers, can be used pulverized fire clay, silica sand, silicaflour, kieselguhr, siliceous fossil deposits in the form of particlesthe most part of which passes a 30 meshes sieve and having an A.F.S.index lower than 100, and refractory fibers such as asbestos.

As combustible material, can be used organic materials having fineparticle size the most part of which passes an 80 mesh sieve and havingan A.F.S. index above 100 to facilitate the combustion and giving a veryfine porosity distributed in the mass, such as broken and crushedresidues from the treatment of cereal grains, in the form of flakedhusks and crushed husks such as husks of wheat, barley, corn, etc.,flakes from grain hulls such as oat hulls, linseed hulls, rice hulls,etc., crushed and broken residues of oil seeds such as lineed, colza,etc., and pulps such as potato and beet and fine sawdust and preferablywood flour.

Crushed hulls are of particular interst as organic combustible materialbecause they give, in the presence of water, a certain quantity ofstarch which augments the agglomerant normally used.

The exothermic products can be the usual exothermic mixtures, aluminiumor magnesium and an alloy aluminium magnesium, but preferably they arethose disclosed in French Pat. No. 1,388,898, Dec. 31, 1963, namely,siliconcalcium alloys or silicon-aluminium alloys mixed with an oxidizerfrom the class consisting of a metallic oxide such as manganese oxideand iron oxide, a salt, such as nitrate, a chlorate and a fluoride ofsodium, potassium and barium.

The agglomeration is preferably effected by means of synthetic resinbinders such as phenolic resins in powdered form or liquid resins suchas urea-formaldehyde resins which are highly concentrated, which is tosay, have a high percentage of solid materials on a dry basis.

By way of example, a semi-exothermic layer may have the followingcomposition the percentage being given by weight.

Percent Silico-calcium or silico-aluminium (the silicon of the alloybeing between 45 and 75% by weight) (being in the form of particles themost part of which passes the 80 meshes sieve with an A.F.S.

index higher than 100) Manganese oxide or iron oxide (being in the formof particles the most part of which passes the 80 meshes sieve with anA.F.S. index higher than 100) a- Chamotte ((pulverized fire clay) (beingin the form of particles the most part of which passes the 30 meshessieve with an A.F.S. index lower than 100) Silica sand or silica powder(being in the form of particles the most part of which passes the 30meshes sieve with an A.F.S. index lower than 100) Kieselguhr orsiliceous fossil deposit (being in the form of particles the most partof which passes the 30 meshes sieve with an A.F.S. index lower than 100)Fine organic materials such as wood flour or husks (being in the form ofparticles the most part of which passes the 70 meshes sieve) 7-15Synthetic resin 5-11 of total amount of the above dry components.

Preferably, and according to another feature of the invention, thesemi-exothermic layer is combined with an exothermic layer in contactwith the cast metal and having the following composition, thepercentages being given by weight:

Percent Silico-calcium or silico-aluminium (the silicon content of thealloy being between 45 and 75 (being in the form of particles the mostpart of which passes the 80 meshes sieve with an A.F.S. index higherthan 100) Manganese oxide or iron oxide (being in the form of particlesthe most part of which passes the 80 meshes sieve with an A.F.S. indexhigher than 100) Chamotte (being in the form of particles the most partof which passes the 30 meshes sieve with an A.F.S. index higher than100) 20-55 Silica sand or silica powder (being in the form of particlesthe most part of which passes the 30 meshes sieve with an A.F.S. indexhigher than 100) Kieselguhr or siliceous fossil (being in the form ofparticles the most part of which passes the 30 meshes sieve with anA.F.S. index higher than 0-9 Finely divided organic materials such aswood flour,

husks, etc. (being in the form of particles the most part of whichpasses the 70 meshes sieve) 8-12 Asbestos fibers O-ll Synthetic resin5l1 of total amount of the above dry componenlts.

The percentage of water introduced may vary from between about 25-700%by weight of the solids. In general, the use of relatively highpercentages of Water 8 desirable when materials are used which areinsoluble or only slightly soluble.

The lining elements may be built up by any known process. For example,filtration may be used. On the filter medium, there is first deposited alayer of the relatively exothermic mixture, after which a layer ofsemi-exothermic mixture is deposited on top of the exothermic layer byfurther filtration of a second solution or suspension. Of course, thelayers could be laid down in the reverse of that order.

The elements can then be fired at C. to eliminate retained water.

As another example, there may be cited a composition for use infabricating the lining for an ingot of 2 tons.

The exothermic layer has a thickness of 5 millimeters and a compositionas follows, the percentages being given by weight and the granulometriesbeing those indicated hereabove for the same materials:

1 7 of the total amount of the above dry components.

The semi-exothermic layer has a thickness of 15 millimeters and formsthe rear or under portion of the lining, with the following composition,the percentages being given by weight and the granulometries being thoseindicated hereabove for the same materials:

Percent Silica sand 33.5 Chamotte 42 Silico-calcium 3 Manganese dioxide3.5 Silica 6 Wood flour l2 Powdered phenolic resin 1 9 of the totalamount of the above dry components.

The two given compositions are mixed with 700% water, based on theweight of the solids, and are deposited one on top of the other by meansof filtration.

A completed lining of the present invention is shown in the drawing. Ona metallic substrate 1 comprising an inner wall of a mold, there issecured a layer 2 of semiexothermic material, and on top of that, alayer of 3 of more highly exothermic material.

From a consideration of the foregoing disclosure, therefore, it will beevident that all of the initially recited objects of the presentinvention have been achieved.

Although the present invention has been described and illustrated inconnection with preferred embodiments, it is to be understood thatmodifications and variations may be resorted to without departing fromthe spirit of the invention, as those skilled in this art may readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the present invention as defined by theappended claim.

What is claimed is:

1. A lining for a metallurgical mold comprising a layer comprised of anagglomerated mixture of 60 to 80 parts in weight of refractory particleshaving an A.F.S. index lower than 100 and interspersed in theinterstices between said refractory particles 7 to 15 parts in weight ofparticles having a 70 mesh fineness of a combustible organic materialselected from the group consisting of grain husks and wood flour, 2.5 to6 parts in weight of particles of readily oxidizable material selectedfrom the class consisting of silicon-calcium alloys and silicon-aluminumalloys containing 45-75% by weight silicon, 2 to 7 parts by weight ofparticles of an oxidizer selected from the class consisting of manganesedioxide and iron oxide, said particles of oxidizable material andoxidizer having an A.F.S. index higher than 100, and a binder selectedfrom the group consisting of phenolic resin and urea-formaldehyde resinin an amount about 5% to about 11% by weight of the total weight of theother dry constituents.

References Cited UNITED STATES PATENTS 3,183,562 5/1965 Moore et a1.3,231,368 1/1966 Watson et a1. 3,273,211 9/1966 Miraldi. 3,297,296 1/1967 Edstrom et al. 3,344,838 10/1967 Nouveau 164-53 FOREIGN PATENTS1,388,898 1/1965 France.

15 LORENZO B. HAYES, Primary Examiner US. Cl. X.R.

Disclaimer 3,582,369.Hen Nou'veau, Saint Germain-les-Corbeil,Seine-et-Oise, France. LININ S F OR STEEL INGOT MOLDS AND FOUNDRY MOLDS.Patent dated June 1, 1971. Disclaimer filed July 15, 1970, by theassignee, Societe Among me Prodm'ts Metallurgz'e Doz'ttau, SA. Herebydisclaims the portion of the term of the patent subsequent to Oct. 3,1984.

[Oficz'al Gazette January 25, 1972.]

